INSECTS, DISEASES, AND INJURIES 133 



water — has given good results when used on nursery trees in 

 the early spring. In England a weak kerosene emulsion is 

 sometimes employed. In case spraying has been neglected 

 till too late in the season, much can be done to reduce the 

 numbers of the lice by cutting off and burning the galls before 

 they open. This method is not to be recommended when 

 spraying is possible. When the trees have become infested in 

 the nursery, it is well to fumigate them before planting out. 



The Colorado blue spruce is also subject to attack by a 

 closely related gall-forming plant-louse {Chermes cooleyi, 

 Gillette). The galls are similar in structure to those caused 

 by the spruce gall aphid, but are more elongate and are at 

 the end of the twig instead of at the base. The same species 

 also attacks Engelmann spruce. Its life history is similar to 

 that of the form previously treated. It may be controlled 

 by the same measures. The fact that this species regularly 

 migrates to red fir and breeds there during part of its life cycle 

 would indicate the undesirability of planting these two conifers 

 on the same or adjoining estates. 



Red and black spruces in the East are likely to have the 

 tips killed by the formation of a tight cone-shaped gall which 

 superficially resembles the true cone of the tree. This gall is 

 produced by a plant-louse {Chermes pinifolicE, Fitch) which 

 spends part of its life cycle on the leaves of the white pine, 

 where it is known as the white pine leaf -aphid. Winged forms 

 appear on the pine in May and June and the next generation 

 settle on the young leaves. The lice are covered with a white 

 waxy secretion which renders them conspicuous. They cause 

 the leaves to turn yellowish and may materially stunt the 

 new growth. 



On spruce this insect may be controlled by removing and 

 destroying the galls before the lice emerge. On pine, spraying 



